The present invention relates to a scroll fluid machine such as a scroll vacuum pump or a scroll compressor.
A scroll fluid machine comprises a housing; a driving shaft having an eccentric axial portion and connected to a driving source, a fixed scroll fixed to the housing and an orbiting scroll which engages with the fixed scroll to form a compression chamber between the fixed and orbiting scrolls. The orbiting scroll is revolved to allow the compression chamber to be reduced in volume toward the center and to enable a gas therein to be compressed.
In JP2006-46078A, between the fixed and orbiting scrolls, a self-rotation preventing device is interposed to allow the orbiting scroll to revolve while it prevents the orbiting scroll from rotating on its own axis. The self-rotation driving device comprises a holder on the outer circumference of the orbiting scroll; a bearing in the holder; a holding plate for holding the bearing in the holder; and a pin crank in which one shaft is rotatably mounted on the bearing while the other shaft is rotatably mounted in the housing.
In the scroll fluid machine, when the orbiting scroll is revolved, excessive load acts to the pin crank in a centrifugal direction when the orbiting scroll is revolved to cause the holding plate to be deformed to make the bearing held unstably. Unstable holding of the bearing makes revolution of the orbiting scroll unstable, so that operation is likely to be inactive. Thus, the holding plate needs to be fixed to the orbiting scroll firmly.